The policy on it should surely be immediately available by searching "big list" on both the FAQ and this meta, right?
No. While it is convenient, there isn't any reason the policy has to be available by searching for a particular keyword. And if there was, it wouldn't be "big list." The thing to search for would probably be "list question," and you'd probably get results by doing it on Meta Stack Overflow.
As for why these questions are not allowed, here are some clues:
Chatty, open-ended questions diminish the usefulness of our site and push other questions off the front page.
Your questions should be reasonably scoped. If you can imagine an entire book that answers your question, you’re asking too much.
To prevent your question from being flagged and possibly removed, avoid asking subjective questions where …
- every answer is equally valid: “What’s your favorite ______?”
- your answer is provided along with the question, and you expect more answers: “I use ______ for ______, what do you use?”
But ultimately, the reason they're not allowed is that they break the Stack Exchange model. List questions are junk food for the site, in a way; they tend to be popular and attract a lot of attention, but they don't provide a basis for judging the correctness of answers (so the voting system is wasted on them) and they never really end, thus drawing attention away from other, better questions.